Scattered radiation grids, also referred to as collimators, for detectors in CT systems are generally known. Until now stacks of thin tungsten plates bonded in a support mechanism were used in CT detectors. These allow the suppression of scattered radiation in the phi direction, in other words in the gantry rotation direction. Until now there was no collimation in the z direction or system axis direction. However it is also known that scattered beam correction is much more effective with a collimator acting in the phi direction and the z direction than with a simple phi collimator, particularly in dual source CT systems. This can be demonstrated by a significant dose reduction for a given contrast/noise ratio or improved artifact reduction.
Also when greater detector z coverage is required, it becomes increasingly difficult to manufacture the support mechanism with enough accuracy to hold the plates in position. If such a phi/z collimator is built in the conventional manner, in other words with individual plates, there is a further problem in that the plates have to be aligned with the focus of the x-ray tube in both directions.
As it is difficult to produce single-piece collimators that extend over the entire detector surface, a modular structure is often used here. One problem with scattered radiation grids of modular structure with a number of adjacent grid modules is that artifacts are produced in the projections recorded therewith in the region of the joining points of two grid modules, having a negative effect on the image quality of a tomographic image data record reconstructed from such projections or producing visible artifacts in the tomographic representation. It is therefore necessary with such collimator modules for different wall thicknesses to be implemented at different positions on the component, for example on the beam exit side or at the edges adjoining adjacent modules.
A collimator structure, in which plates embodied in the manner of combs are intermeshed, is also known from the publication DE 10 2005 044 650 B4. This method is complex and is also made problematic in that the plates should be aligned with the focus.
It is also known from the publication US 2008/0023636 A1 that polymers filled with metal particles can be made to harden in a grid-type form. The disadvantage of this method is the limited fill level of the compound at around 50%, which significantly reduces the collimation effect due to the reduced absorption capacity.
It is further proposed in publication DE 10 2010 011 581 A1 that the walls in both directions should be produced by selective laser melting SLM. SLM is a method in which metallic components can be produced in almost any complex geometries directly from 3D CAD data. It involves many layers of powdered metal being melted selectively one above the other using a laser beam based on the calculated surfaces, until the desired structure is produced. The method is such that the structures produced in this manner have very rough surfaces, which have to be further processed by way of a series of subsequent processes. Also it is not always possible to achieve all the desired wall thicknesses.